CV6099 image converter tube. These are sensitive to infrared light out to
a wavelength of about 1 micron but the luminous gain of systems using them is
approximately 1, so a source of infrared light would be needed if they were
being used at night. They were developed in the late 1950s and are essentially
an improved version of image converter tubes used as far back as 1934. They
were typically used throuhgout the 1960s in various pocketscopes, binoculars,
tank periscopes etc., and were replaced through the 1970s and 1980s by image
intensifiers using ambient light and by thermal imaging systems.